This application claims priority from Korean Patent Application No. 2003-54778, filed on Aug. 7, 2003, and No. 2004-10414, filed on Feb. 17, 2004 in the Korean Intellectual Property Office, the disclosures of which are incorporated herein in their entirety by reference.
1. Field of the Invention
The present invention relates to an organometallic compound that contains iridium (Ir) and an organic electroluminescent device using the same, and more particularly, to an iridium compound that may be used as a blue phosphorescent material and an organic electroluminescent device using the same.
2. Description of the Related Art
Electroluminescent (EL) devices, known as self-luminous displays, have the advantages of large viewing angle, high contrast, and short response time. EL devices can be classified depending on the material used for the emissive layer as inorganic or organic EL devices. As compared with inorganic EL devices, organic EL devices have the advantages of higher luminance, lower driving voltage, shorter response time, and the ability to display a wider range of colors.
A typical organic EL device includes an anode on the top surface of a substrate. A hole transporting layer, an emissive layer, an electron transporting layer, and a cathode are formed sequentially on the anode. The hole transporting layer, the emissive layer, and the electron transporting layer are thin films made of organic compounds.
Organic EL devices with the above-described structure operate according to the following principles. When a voltage is applied across the anode and the cathode, holes injected from the anode migrate via the hole transporting layer into the emissive layer. Electrons injected from the cathode migrate via the electron transporting layer into the emissive layer and combine with the holes therein to generate exitons. When the exitons transit from excited state to base state, molecules in the emissive layer emit light to form visible images.
Materials for the emissive layer can be classified depending on their light emission mechanism as fluorescent materials that emit light from exitons in a singlet state or phosphorescent materials that emit light from exitons in a triplet state. In general, phosphorescent materials are organometallic compounds that contain a heavy atom and an organic ligand. In phosphorescence from phosphorescent materials, exitons which are in a non-emissive triplet state due to the heavy atom are allowed to change state and participate in emission. Such phosphorescent materials use 75% of triplet state exitons for emission and offer higher luminescent efficiency compared to fluorescent materials that use only 25% of singlet state exitions for emission.
A number of triple state phosphorescent materials, such as metallic compounds, for example, iridium and platinum, have been reported. Blue phosphorescent materials developed so far include (4,6-F2 ppy)2Irpic, Ir compounds with a fluorinated ppy ligand structure, etc. However, these materials emit light in a sky blue range and lack suitable host materials, thereby leading to very low efficiency and short lifetime compared to red and green phosphorescent materials. Therefore, there is an urgent need for the development of deep blue, high-efficiency, long lifespan phosphorescent materials.